Terahertz absorption spectrum of para and ortho water vapors at different humidities at room temperature
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Terahertz time-domain spectroscopy has been used to measure the absorption of water vapor in 0.2–2.4THz range from low to high humidity at room temperature. The observed absorption lines are due to the water molecular rotations in the ground vibrational state. We find that the absorption strength of para transitions increases as humidity increases, while the absorption strength of ortho transitions increases and then decreases in intensity with increasing humidity. We explain this difference based on the nuclear spin statistics based ratio of ortho to para water monomer populations at room temperature. The preferential adsorption on the solid surfaces of para water leads to an ortho dominated vapor cloud whose monomer rotational absorption intensity decreases due to the effects of dimerization, molecular collisions, clustering, and interactions with liquid droplets at high concentrations.
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Variations in atmospheric temperature, pressure, or humidity cause the attenuation and dispersion of THz radiation to change at frequencies close to absorption lines.
“Variations in atmospheric temperature, pressure, or humidity cause the attenuation and dispersion of THz radiation to change at frequencies close to the numerous absorption lines in this frequency band.”
From Dual-Beam THz Spectrometer with Low-Aberration Optics and Off-Axis Multipixel Photoconductive Emitters for Reduced Systematic Errors (2025) · cites this paper as [23]
Working under standard atmospheric conditions presents challenges for THz spectroscopy, imaging, and communications because of the rotational modes of water vapor.
“Working under standard atmospheric conditions presents challenges for THz spectroscopy, imaging, and communications because of the rotational modes of water vapor.23,24”
From Dual-Beam THz Spectrometer with Low-Aberration Optics and Off-Axis Multipixel Photoconductive Emitters for Reduced Systematic Errors (2025) · cites this paper as [23]
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References 18 · Cited by 116
Research works printed but not linked: 1
- J.-M. Flaud, C. Camy-Peyret, and R. A. Toth, International Tables of Selected Constants ͑Pergamon, Oxford, 1987͒.
- Authors
- Xin, X., Altan, H., Saint, A., Matten, D., & Alfano, R. R.
- Affiliations
- City College of New York (US)
- Venue
- Journal of Applied Physics
- Publisher
- AIP Publishing
- Published
- 2006-11-01
- Volume
- 100
- Issue
- 9
- ISSN
- 0021-8979 (ISSN-L)
- 1089-7550
- OpenAlex
- W2026985493
- Cited by
- 116
- References
- 18
- Citations by year
- 2026: 5 · 2025: 6 · 2024: 9 · 2023: 12 · 2022: 13 · 2021: 5 · 2020: 8 · 2019: 5 · 2018: 10 · 2017: 7 · 2016: 2 · 2015: 6 · 2014: 4 · 2013: 4 · 2012: 3
- FWCI
- 4.38
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Journal of Applied Physics (publishedVersion)
- ScholarSphere (Penn State Libraries) (submittedVersion)
- OpenMETU (Middle East Technical University) (submittedVersion, cc-by-nc-nd)
- Funders
- National Aeronautics and Space Administration
- Carnegie Corporation of New York
- Topics
- Physical Sciences › Engineering › Electrical and Electronic Engineering › Terahertz technology and applications
- Physical Sciences › Chemistry › Spectroscopy › Spectroscopy and Laser Applications
- Physical Sciences › Chemistry › Spectroscopy › Molecular Spectroscopy and Structure
- Keywords
- water vapor, terahertz absorption, nuclear spin statistics, humidity dependence, ground vibrational state, rotational transitions, molecular clustering, surface adsorption, room temperature
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